In this paper, the composite foam material with epoxy resin as matrix and polymer microspheres as filler is added with voltage stabilizer RBBT, and its effect on electrical properties is tested by partial discharge experiment. Four gradient samples were prepared in the experiment. 0%, 2%, 4%, 6% mass fraction voltage stabilizer RBBT was added to the epoxy resin composite foam material as the base, and the needle electrode was embedded in the sample to simulate the extremely uneven electric field. The partial discharge test platform was set up, and the partial discharge test was carried out on epoxy resin composite foam by the stepwise voltage boost method, and the influence of voltage stabilizer with different mass fraction on the electric resistance of composite foam was analyzed. The results show that the breakdown voltage can be greatly improved by adding 6% mass fraction voltage stabilizer RBBT.